Urine Drug Testing: Immunoassay vs. Laboratory Testing

Michael Schatman, PhD, CPE

In last month’s Pain Perspectives, I discussed algorithms for stratifying levels of risk utilizing urine drug testing (UDT). This month’s column will discuss immunoassay and laboratory testing, and focus on their appropriate role in opioid risk mitigation.

Immunoassay (also known as “point-of-care” or “office collection”) testing should always be considered the first step in a sound UDT program. This type of testing quickly and efficiently identifies specific drugs or metabolites utilizing antibodies (1). It is important to note, however, that immunoassays are best suited as screening tests; their diagnostic inaccuracy and the risk of false-positive or false-negative results render them subject to possible misinterpretation (2).

Accordingly, immunoassay results should only be considered presumptive. Given this, why should immunoassay testing be conducted at all? The bottom line is… the bottom line. The ease of use and the low cost of immunoassay testing makes it a practical and ethical first step. Until such time that the United States follows the rest of the industrialized world and adopts a system of universal health care, the health insurance industry will be a “necessary evil”, and their reimbursement for UDT will remain essential.

For many years, unscrupulous providers engaged in the practice of “unbundling” — charging patients and their insurers separately for each substance for which they screened.. (3). UDT began to be seen as a “cash cow” rather than as a means of protecting patients as well as physician practices. As Zhang and Kwong (4) recently noted, insurance payers have become less than supportive of UDT. In response to such profiteering, the Centers for Medicare and Medicaid Services (CMS) modified its reimbursement policy in 2011 in an effort to to stop this self-serving practice. However, private payers have been inconsistent in enforcing the unbundling approach, and despite the risk for formidable penalties, some providers continue to bill inappropriately.

Urine drug testing companies have their own sophisticated laboratories which perform UDT with greater accuracy than that provided by in-office immunoassay screening. If this is the case, why not send all samples for laboratory testing? Again, cost considerations and the insurance industry’s willingness to reimburse for testing needs to be taken into account. In a recent article, Reisfield and Maschke (5) noted that point-of-collection testing costs in the range of $5 per sample, with commercial carriers reimbursing in the range of $10-$18 per sample.

When an immunoassay test is inconsistent (i.e. indicating the presence of a prescription or illicit drug that should not be in the sample, or, conversely, not containing evidence of a medication that should be in the sample), more expensive and accurate confirmation testing should be conducted. According to a large retrospective study (6), between 3 and 5% of screening results should be sent for confirmation testing.

From an ethical perspective, confirmation testing should be performed on all inconsistent immunoassays, as the repercussions of a false-positive screen can be dramatic. Confirmation testing was typically conducted through gas chromatography/mass spectrometry (GC/MS), although recent advances in technologies such as liquid chromatography-tandem mass spectrometry (LC-MS/MS) are beginning to bring about a paradigmatic revision in laboratory practices. Importantly, the validity for extreme accuracy of both of these types of testing has been established (2,7).

Next month, I will discuss the challenges involved in accurately interpreting the results of UDT, the role of the laboratory that you use in assisting you, and how to discuss these results with your patients in a meaningful and productive manner. In the meantime, keep your patients comfortable and safe, and keep the faith!

References

1) Moeller KE, Lee KC, Kissack JC. Urine drug screening: practical guide for clinicians. Mayo Clin Proc. 2008;83:66-76.

2) Manchikanti L, Malla Y, Wargo BW, et al. Protocol for accuracy of point of care (POC) or in-office urine drug testing (immunoassay) in chronic pain patients: a prospective analysis of immunoassay and liquid chromatography tandem mass spectrometry (LC/MS/MS). Pain Physician 2010;13:E1-E22.

3) Collen M. Profit-driven drug testing. J Pain Palliat Care Pharmacother. 2012;26:13-17.

4) Zhang Y, Kwong TC. Utilization management in toxicology. Clinica Chimica Acta 2014;427:158-166.

5) Reisfield GM, Maschke KJ. Urine drug testing in long-term opioid therapy: ethical considerations. Clin J Pain 2014;30:679-684.

6) Gilbert JW, Wheeler GR, Mick GE, et al. Urine drug testing in the treatment of chronic noncancer pain in a Kentucky private neuroscience practice: the potential effect of Medicare benefit changes in Kentucky. Pain Physician 2010;13:187—194.

7) Krone N, Hughes BA, Lavery GG, Stewart PM, Arlt W, Shackleton CH. Gas chromatography/mass spectrometry (GC/MS) remains a pre-eminent discovery tool in clinical steroid investigations even in the era of fast liquid chromatography tandem mass spectrometry (LC/MS/MS). J Steroid Biochem Mol Biol. 2010;121:496-504.